# Is it possible to have an universal RF receiver and transmitter (Wifi / Bluetooth)

First of I should make clear that I'm not an engineer. My friends who are helping me with this project are. But me.. well lets just say I know the basics.

Problem

I have to be honest, it's a first world problem but nevertheless a problem. Most of my devices that are connected to my tv are in my livingroom(groundfloor). I have a setup which allows me to send the image of all my devices to my bedroom which is on the firstfloor approximately 30ft (10 meters) away. the problem is that some of my devices are not receiving the bluetooth/wifi signals from the remote/controllers (bluetooth/wifi). Offcourse that's not very surprising.

Solution

We have been searching the web for quite some time but we are unable to find a bluetooth range extender/repeater.

To put in layman's terms; we thought that it might be possible to create a device that has an antenna which receives all RF signals (bluetooth and wifi are RF signals) and sends all received signals to a base unit which stands next to the equipment or extend/repeat the signal so it reaches the devices on the groundfloor. This device will not alter the signals in any way. Just transfer it back and forth as it is.

Are we completely crazy or is this possible. And if so, what do we need.

Thanks for reading and even the smallest push in the right direction is much appreciated!

Practically speaking, no.

Theoretically yes, but it gets tricky.

If you only needed to do one way communication, you could build a pure-analog system which would just receive a chunk of the 2.4 GHz band, amplify it without caring to understand the detail, shove it down a suitable transmission line, and push it out an antenna at the other end.

The problem is that most of your devices are bidirectional. If they were bidirectional with a range of frequencies reserved in each direction, you could use two instances of same trick as above, with careful filtering to separate the upstairs vs. downstairs frequency ranges and avoid looping feedback signals through the system.

But that's not how these services mostly work - they are bidirectional on the same frequencies, taking turns in time (or at least the transmit and receive channels are intermixed). To relay this requires something that actually understands the protocols of all the services involved. In theory, a sufficiently smart software defined radio could receive the entire band, process all transmissions for all known protocols, decide which should be repeated upstairs or downstairs, and send that over a cable for its partner in the other location to re-transmit.

In practice, this is too complicated. You are better off using existing per-protocol solutions. For example, you can get wifi hotspots that are designed to work together, interconnected by an ethernet cable, and route traffic between their respective peers.

Bluetooth repeaters seem conceptually a bit trickier, but might exist.

Ultimately, the possibility of buying these off the shelf is not a question that would be on topic here; what I have tried to do is give you an engineering answer as to why a universal system would be hard to build yourself, and why it is probably not on the market.

• Hi Chris,Thanks for taking the time. I really appreciate the feedback. Back to the drawing table it is. – Don Molenaar Aug 6 '14 at 17:08

In addition to what Chris said, another difficulty with regard to many wireless protocols is that devices which send packets and expect a response generally expect that response to be sent at a specific time. If a device expects to receive a response to a packet 1000us+/-150us after it is sent, and a device which receives the packet will send out a response 1000us+/-100us later, then it will be necessary to ensure that the round-trip time be extended by no more than 50us. Given that packets some packets will take 50us or longer to send, it would be necessary for the repeater to commence the retransmission of each packet even before the original transmission was finished. Even under the best of circumstances (assuming a receiver that can continue to hear the original transmitter even while the relay transmitter is operating on the same frequency), that would be very difficult. Under more realistic circumstances, it's impossible.

• This is a concern, yes (I'd thought only of the increase in propagation time, not that the packet length could exceed it), but it seems to me that since the retransmitter will be remote from the proxying receiver compared to the original, careful choice of power levels may solve that problem. It's not clear that the proxying system needs to wait for the end of a transmission to start relaying, but it does point to not using a packetized scheme on the wire, or at least if using one, using wire packets that can contain small pieces of an RF packet. – Chris Stratton Aug 6 '14 at 17:12
• @ChrisStratton: Even if the two ends are far enough apart not to interfere (a very generous assumption), a relay point shouldn't try to pass along a transmission until it knows what it is. While some protocols precede each packet with enough of a preamble that a receiver can be pretty confident that an unsolicited packet of its desired protocol is about to arrive, some low-energy protocols use a very short pre-amble. This means that receivers will frequently misinterpret pieces of other unrelated transmissions as start-of-packet indicators, but having protocols deal with that is cheaper... – supercat Aug 6 '14 at 17:42
• ...than using a longer preamble. Unfortunately, it also means that it may not be possible to reliably determine whether something is a transmission in a particular format until the whole thing has been received. – supercat Aug 6 '14 at 17:43
• "a relay point shouldn't try to pass along a transmission until it knows what it is" why? All it really needs to know is that it looks like the start of a valid packet. It might not be, but having a fragment recreated at the far end doesn't seem more harmful than the one at the existing end. The exception would be if there is mid-packet collision detection, but I don't think that is done on radio links of this sort, as a transmitter would blind its own receiver. – Chris Stratton Aug 6 '14 at 18:26
• @ChrisStratton: Many kinds of digital signals are not terribly robust against "analog" degradation; it is expected that devices which relay a signal will correct any deviations from ideal before passing it along. Doing that, however, requires knowing what the "ideal" is. The bit pattern 11001100 sent at 2mbps and sending the bit pattern 1010 at 1mbps would have the same "idealized" digital waveform, but the latter would be "smoothed" more prior to transmission. Smoothing the former signal would increase the risk that it might get misinterpreted as something like 11101110 or 10001000, but... – supercat Aug 6 '14 at 19:11